Section 5 The Theory of Plate Tectonics

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Vocabulary

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scientific theory- a well- tested concept that explains a wide range of observations.
plate tectonics- the geologic theory that states that piece of Earth's lithosphere are in constant, slow motion, driven by convection currents in the mantle.
transform boundary- a place where two plates slip past each other, moving in opposite directions.
divergent boundary- a place where two plates move apart.
convergent boundary- a place where two plates come together.
rift valley- when continental plates pull apart at a divergent boundry on land, this forms.

Outline

A Theory of Plate Motion

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• plates move slowly by the convection currents.
• as plates move, different things happens.
  • they can collide, pull apart, or grind each other.
• change also happens to the plates.
  • volcanoes can be formed.
  • mountain ranges can be made.
  • deep- sea trenches also can form.

Plate Boundries

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• There are three types of plate boundaries.
  • Transform Boundary
    • they slip past each other moving in opposite directions.
  • Dirvergent Boundary
    • they move apart.
    • rift valley can be formed.
  • Converagant Boundary
    • two plates come together
    • when they converge, a collision occurs
• oceanic crust and continental crust
• oceanic crust and oceanic crust
• continental crust and continental crust
• when they collide one subducts into a deep- ocean trench

The Continent's Slow Dance

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• moving at a slow rate
  • about 1-10 centimeters a year
• North America, and Eurasia are moving apart
  • at the rate of 2.5 cm.
• continents were once one great landmass
  • 225 million years ago this great landmass started to break apart